Magnetic iron-dextran microspheres

Abstract

The invention relates to colloidal sized particles composed of magnetic iron oxide (Fe3O4) coated with a polysaccharide, preferably dextran, or a derivative thereof having pendant functional groups. The particles have a magnetic moment, are electron dense, and are stable and non-aggregating under physiological conditions. They can be covalently bonded to antibodies, enzymes and other biological molecules and used to label and separate cells, cellular membranes and other biological particles and molecules by means of a magnetic field.

What is claimed is: 
     
       1. Discrete colloidal sized particles having a core of ferromagnetic iron oxide (Fe 3  O 4 ) and coated with a water-soluble polysaccharide or a derivative thereof having pendant functional groups. 
     
     
       2. Particles as claimed in claim 1 having a diameter of about 100 to about 700 Å. 
     
     
       3. Particles as claimed in claim 1 having a diameter of about 300 to about 400 Å. 
     
     
       4. Particles as claimed in claim 1 wherein the polysaccharide is dextran. 
     
     
       5. Particles as claimed in claim 1 which have pendant aldehyde functional groups. 
     
     
       6. Particles as claimed in claim 1 which have pendant amino functional groups. 
     
     
       7. Particles as claimed in claim 1, 5 or 6 to which are attached biological molecules or particles bonded to functional groups of the polysaccharide or polysaccharide derivative. 
     
     
       8. Particles as claimed in claim 1 or 5 to which are attached a protein bonded to functional groups of the polysaccharide or polysaccharide derivative. 
     
     
       9. Particles as claimed in claim 5 to whose aldehyde functional groups is attached the protein S. Aureus Protein A. 
     
     
       10. Particles as claimed in claim 5 to whose aldehyde functional groups is attached immunoglobulin. 
     
     
       11. Particles as claimed in claim 1, 5 or 6 to which are attached biological molecules or particles selected from the group consisting of antibodies, cells, enzymes, drugs, toxins, hormones and nucleic acids. 
     
     
       12. Particles as claimed in claim 9 or 10 wherein there are attached to the protein biological particles selected from the group consisting of antibodies, cells, enzymes, drugs, toxins, hormones and nucleic acids. 
     
     
       13. A process for preparing colloidal sized particles as claimed in claim 1 which comprises mixing a water-soluble polysaccharide or a derivative thereof having pendant functional groups with an aqueous solution containing ferrous and ferric salts, adding alkali to the solution and separating polysaccharide- or polysaccharide derivative-coated ferromagnetic iron oxide particles. 
     
     
       14. A process according to claim 13 wherein the ferrous and ferric salts are ferrous and ferric chlorides. 
     
     
       15. A process according to claim 13 wherein aqueous ammonium hydroxide is added dropwise to the solution of ferrous and ferric salts to raise the pH to a value in the range of from 10 to 11. 
     
     
       16. A process according to claim 10 wherein the polysaccharide is dextran having an average molecular weight of between about 10,000 and about 70,000. 
     
     
       17. A process according to claim 13 wherein a polysaccharide at least some of whose hydroxyl groups have been oxidized to aldehyde group is mixed with the aqueous solution of ferrous and ferric salts, to obtain particles having pendant aldehyde functional groups. 
     
     
       18. A process according to claim 10 wherein a polysaccharide is mixed with the aqueous solution of ferrous and ferric salts and the process comprises the further step of oxidizing the polysaccharide coated particles to form pendant aldehyde functional groups. 
     
     
       19. A process according to claim 13 which comprises the further step of reacting a polysaccharide coated particle having pendant aldehyde functional groups with an amino-group containing molecule to form a Schiff base and then reducing the Schiff base so that the amino-group containing molecule is stably attached to the polysaccharide coated particle. 
     
     
       20. A process according to claim 19 wherein the amino-group containing molecule is a protein. 
     
     
       21. A process according to claim 20 wherein the protein is S. Aureus Protein A. 
     
     
       22. A process according to claim 20 wherein the protein is immunoglobulin. 
     
     
       23. A process according to claim 19 wherein the amino-group containing molecule is an α,ω-alkylene diamine and the process comprises the further step of reacting the obtained polysaccharide coated particles having pendant amino functional groups with an α,ω-dialdehyde, followed by reduction to obtain polysaccharide coated particles having pendant aldehyde groups. 
     
     
       24. A process according to claim 19 wherein the amino-group containing molecule is diaminoethane or diaminoheptane and the process comprises the further step of reacting the obtained polysaccharide coated particles having pendant amino functional groups with glutaraldehyde, followed by reduction to obtain polysaccharide coated particles having pendant aldehyde groups. 
     
     
       25. A process according to claim 13 which comprises the further step of reacting the product with biological particles selected from the group consisting of antibodies, cells, enzymes, drugs, toxins, hormones and nucleic acids. 
     
     
       26. A method of separating a required antigen from a population of antigens which comprises introducing into the population of antigens discrete colloidal sized particles having a core of ferromagnetic iron oxide and coated with a polysaccharide or a derivative thereof to which is attached an antibody specific to the required antigen, so that there are formed antigen-antibody conjugates on the particles, separating the particles by magnetic means and subsequently dissociating the antigen-antibody conjugate, to obtain the required antigen. 
     
     
       27. A method according to claim 26 wherein the antigen-antibody conjugate is dissociated by reaction with sodium thiocyanate, by reaction with urea, by acidification or by digestion with a proteolytic enzyme. 
     
     
       28. A method of treating a tumour which comprises introducing into the patient having the tumor a cytotoxic drug attached to discrete colloidal sized particles having a core of ferromagnetic iron oxide and coated with a polysaccharide and applying an external magnetic field to localize the particles bearing the cytotoxic drug in the region of the tumour. 
     
     
       29. A method of labeling cells, enzymes, toxins, hormones, lectins, growth factors, nucleic acids or radiosotopes, discrete colloidal sized particles having a core of ferromagnetic iron oxide and coated with a polysaccharide or a derivative thereof having pendant functional groups, the particles being attached to the cells, enzymes, toxins, hormones, lectins, growth factors, nucleic acids or radioisotopes via the functional group. 
     
     
       30. A method according to claim 29 which comprises the further step of separating labeled cells, enzymes, toxins, hormones, lectins, growth factors, nucleic acids or radioisotopes attached to the particles of ferromagnetic iron oxide by magnetic means. 
     
     
       31. A method of cleaning water contaminated with an undesirable chemical agent which comprises adding to the water discrete colloidal sized particles having a core of ferromagnetic iron oxide and coated with a polysaccharide or a derivative thereof having pendant functional groups to which is attached a proteolytic enzyme which will digest the undesirable chemical agent, and recovering the particles by magnetic means.